Power screwdrivers are commonly used in manufacturing assembly lines to insert and drive screws, bolts and other turn-in fasteners quickly and accurately. An assembly line operator may drive as many as 7,000 screws during a normal work day. Typically, powered screwdrivers are heavy hand operated pneumatic or electrical units. To reduce operator fatigue, mechanical support arms have been developed to carry the weight of the drivers, while allowing the operators to manipulate the screwdrivers in a full range of motion. Generally, a support arm includes a pair of universal joints and a telescoping member to support the screwdriver from a wall ceiling or a stationary stand. A tensioning device supports the weight of the screwdriver and helps maintain the support arm at the correct attitude. The operator may grasp and manipulate the screwdriver to any operational position.
As commonly known, the universal joints of the mechanical arm allow limited freedom of movement in any direction, but permit full 360.degree. rotational movement. Consequently, the rotational moment generated by the driver is transmitted directly into the telescoping member. Conventional telescoping members permit the extensible rod to rotate freely with the outer housings. Consequently at the penetration limit of the screw, the rotational torque generated by the power screwdriver is absorbed and arrested by the operator's hand. In high volume operations common in manufacturing assembly lines, the repetitious physical stress of absorbing the transferred rotation torque leads to various overuse injuries in the ligaments and tendons in the wrist and hand, and fatigues the operators, which reduces productivity.